The present invention relates to a ring-like hydraulic dynamic pressure bearing having axial dynamic pressure portions and radial dynamic pressure portions alternately contiguous to each other and a spindle motor using this bearing.
There is used a hydraulic dynamic pressure bearing having a shaft portion and a bearing portion for supporting the shaft portion, formed with dynamic pressure generating grooves at either of the opposed faces of the two portions above and forming a layer of a lubricant at high pressure in the very small clearance between the two portions through the rotation of the shaft portion, to thereby realize noncontact rotation of the shaft portion, as a bearing of a spindle motor of a hard disk device.
FIG. 8 is a sectional view showing a conventional ring-like hydraulic dynamic pressure bearing. A ring-like hydraulic dynamic pressure bearing 100 is provided with a shaft portion 103 constituted by fixing a ring 102 to an end portion 101A of a shaft main body 101 by press fitting and a bearing portion 104 supporting the shaft portion 103 and constituted such that the ring 102 at the shaft portion 103 rotatably contained in a recessed portion 105A of a main body 105 of the bearing portion 104 is prevented from coming out from the recessed portion 105A by a circular disk thrust resisting member 106.
An upper face 102A and a lower face 102B of the ring 102 are provided with axial dynamic pressure generating grooves G1 and G2 respectively, and the outer peripheral face 102C of the ring 102 is provided with radial dynamic pressure generating grooves G3.
A lubricant for generating dynamic pressure is held between the shaft portion 103 and the bearing portion 104 and accordingly, when the shaft portion 103 is rotated, axial dynamic pressure is generated between the upper face 102A and the circular disk-like thrust holding member 106 by the axial dynamic pressure generating grooves G1 and axial dynamic pressure is generated between the lower face 102B and a bottom face of the recessed portion 105A by the axial dynamic pressure generating grooves G2. Further, radial dynamic pressure is generated between the peripheral face 102C and an inner peripheral face of the recessed portion 105A by the radial dynamic pressure generating grooves G3. As a result, axial dynamic pressure bearings and a radial dynamic pressure bearing which are lubricant layers at high pressure are formed between the shaft portion 103 and the bearing portion 104 to thereby enable rotation of the shaft portion 103 by noncontact rotation.
As described above, according to the conventional ring-like radial dynamic pressure bearing, there is constructed the constitution in which the radial dynamic pressure generating face and the axial dynamic pressure generating faces are contiguous to each other and accordingly, the following problem is posed: when the shaft portion 103 is rotated, because of the axial dynamic pressure generating grooves G1, the axial dynamic pressure generating grooves G2 and the radial dynamic pressure generating grooves G3 which are respectively formed at the upper face 102A, the lower face 102B and the peripheral face 102C of the ring 102, the lubricant is drawn to central portions of the respective dynamic pressure generating faces and negative pressure is produced at portions of the upper face 102A and the peripheral face 102C contiguous to each other and portions of the lower face 102B and the peripheral face 102C contiguous to each other. As a result of producing the negative pressure caused by mutual interference, air bubbles are liable to be generated at the portions of the dynamic pressure generating faces contiguous to each other and hamper flow of the lubricant and accordingly, an unfavorable condition may occur in which sufficient dynamic pressure is not generated and the bearing rigidity is deteriorated.
Hence, it is an object of the invention to provide a hydraulic dynamic pressure bearing capable of resolving the above-described problem in the conventional technology and a spindle motor using the above bearing.
In order to resolve the above-described problem, according to an aspect of the invention, there is proposed a hydraulic dynamic pressure bearing which is a ring-like hydraulic dynamic pressure bearing comprising a shaft portion constituted by fixing a ring to an end portion of a shaft main body thereof and a bearing portion supporting the shaft portion via the ring and formed with a radial dynamic pressure bearing portion and axial dynamic pressure bearing portions contiguous to each other between the ring and the bearing portion wherein ring-like spaces for storing a lubricant for generating dynamic pressure are provided along portions where the radial dynamic pressure bearing portion and the axial dynamic pressure bearing portions are contiguous to each other and the ring-like spaces are maintained at an atmospheric pressure.
When relative rotational motion is produced between the shaft portion and the bearing portion, lubricant in the respective dynamic pressure bearing portions is drawn to respective central portions of these to thereby generate required dynamic pressure. Therefore, at regions of the radial dynamic pressure bearing portion and the axial dynamic pressure bearing portions contiguous to each other, the lubricant is going to be reduced. Lubricant is stored at the ring-like spaces provided along contiguous portions of two dynamic pressure bearing portions, the inside of the ring-like spaces kept at atmospheric pressure, and accordingly the lubricant which is needed in the dynamic pressure bearing portions is smoothly supplied from the inside of the ring-like spaces. Therefore, mutual interference is not produced between the two dynamic pressure bearing portions. As a result, negative pressure is not generated at portions of the two dynamic pressure bearing portions contiguous to each other and no air bubbles are produced in the lubricant and accordingly, the bearing rigidity can be made higher than that of the conventional bearing.
The radial dynamic pressure bearing can be formed by providing dynamic pressure generating grooves at an outer peripheral face of the ring on an inner face of the bearing portion opposed thereto. The axial dynamic pressure bearing can be formed by providing dynamic pressure generating grooves at at least one of the plane portions contiguous to the outer peripheral face of the ring. Or, the dynamic pressure generating grooves may be formed at inner faces of the bearing portion opposed to the plane portions.
The spaces for storing the lubricant can be provided by forming ring-like recessed portions at boundary regions between the outer peripheral face of the ring and the planes contiguous thereto. The cross-sectional shape of the recessed portion may be that of a circular arc or an arbitrary stepped L-like shape.
In order to maintain the ring-like spaces for storing the lubricant at the atmospheric pressure, communicating means for communicating the spaces with the atmosphere can be formed at the bearing portion. Constricted passages are provided in the communicating means to thereby prevent the lubricant from leaking from the ring-like spaces to outside.
Further, according to another aspect of the invention, there is proposed a constitution in which a clearance is provided between an end face of the shaft main body and the bearing portion opposed thereto and paths at the inner peripheral face for communicating with the clearance with the atmosphere are formed to thereby enable circulation of a lubricant through the above clearance and the circulating paths.
According to the constitution, in the case in which there is constructed a constitution in which axial dynamic pressure is generated between the plane portion on an end face side of the shaft main body and the plane portion of the bearing, even when the lubricant disposed in the clearance is drawn to the ring side in generating the dynamic pressure, owing to the lubricant circulating to the clearance by passing through the paths communicating with the atmosphere, negative pressure can effectively be prevented from generating in the clearance. As a result, the dynamic pressure is satisfactorily generated at the plane portion and the bearing rigidity can further be promoted.
Further, in either case, the ring-like space for storing the lubricant is not limited to a constitution provided by machining the ring, but in place thereof or in addition thereto, there may be constructed a constitution provided by, for example, a ring-like groove at a corresponding portion of the bearing portion.